1. Field of the Invention
The present invention relates to a control apparatus for controlling an automotive generator installed on a vehicle according to field switching rate of a field circuit of the generator and, more particularly, the invention pertains to an automotive generator control apparatus which can perform operation for averaging changing values of field switching rate with a simple configuration.
2. Description of the Background Art
Conventionally, an electronic control unit (ECU) for controlling a vehicle engine monitors field switching rate (or field coil duty factor) of an automotive generator. The ECU controls field current ON/OFF states to maintain the amount of power generated by the automotive generator at a proper level based on a field coil duty factor signal (hereinafter referred to as the DF signal) which is generated by a regulator of the generator.
Generally, the DF signal directly indicates ON/OFF (conducted or non-conducted) states of a field current switching device, or a switching transistor. Switching on/off operation of the switching transistor serving as the field current switching device is controlled by a pulse width modulation (PWM) control method performed at a frequency of about 50 Hz to 200 Hz by the regulator, wherein the field coil duty factor normally varies from one cycle to next of PWM control operation. In most cases, the DF signal takes erratically changing values, such as 50%, 70%, 10%, and so on, over successive PWM control operation cycles while the generator is in operation.
Since the DF signal, which is an input parameter for controlling the generator, takes such erratically changing values even if the DF signal is monitored at intervals of a specific number of PWM control operation cycles, operation for controlling the generator is apt to become unstable and unreliable.
Therefore, if the DF signal of which value varies so significantly is to be used for controlling the generator, it is necessary to perform a certain form or averaging operation.
For example, Japanese Laid-open Utility Model Publication No. 1985-181200 discloses an arrangement for solving the aforementioned problem, in which a DF signal is transmitted to an ECU and values of the DF signal are processed by a mathematical operation performed by the ECU to produce a control parameter used for controlling a generator.
On the other hand, Japanese Laid-open Patent Application No. 2001-258295 discloses an arrangement for solving the aforementioned problem, in which a generator regulator includes as means for reading a DF signal on the regulator side an averaging circuit including an average value latch circuit such that effects of an input signal of which recurring cycles have been disturbed by external noise would be mitigated.
When applied to a control apparatus for controlling an automotive generator by use of the DF signal, the aforementioned arrangement of Japanese Laid-open Utility Model Publication No. 1985-181200 has a problem that the ECU must take great work load in executing the mathematical operation needed for producing an easy-to-use control parameter from the DF signal, for example.
The aforementioned arrangement of Japanese Laid-open Patent Application No. 2001-258295 when applied to an automotive generator control apparatus requires the provision of an averaging circuit including an average value latch circuit. Although the conventional averaging circuit can efficiently smooth out changing values of the DF signal, it is necessary to install a memory having a large storage capacity. Additionally, the averaging circuit must have an adder circuit and a subtracter circuit and, thus, this approach results in an increase in circuit scale and an eventual cost increase.